# Systemd

{% embed url="<https://en.wikipedia.org/wiki/Systemd>" %}
(wikipedia.org)
{% endembed %}

In the following text [an example service](broken://pages/-M4krqA0gfAnLYA6KGUR) named `vultrdata` is used for illustrative purposes.

A service is defined in a file named like `/etc/systemd/system/vultrdata.service`. Unit files have a format like in this example:

```
[Unit]
Description=Vultr Instance Metadata Service
After=network.target

[Service]
User=vultrdata
WorkingDirectory=/opt/vultrdata
Restart=always
Environment=API_KEY=____________________________________
ExecStart=/opt/vultrdata/vultrdata --addr 10.1.2.3 --port 8888 --userdata

[Install]
WantedBy=multi-user.target
```

After creating the file in the `/etc/systemd/system` directory, issue this command to register it:

```
$ sudo systemctl daemon-reload
```

Then you can check the status:

```
$ sudo systemctl status vultrdata
● vultrdata.service - Vultr Instance Data Service
   Loaded: loaded (/etc/systemd/system/vultrdata.service; disabled; vendor preset: enabled)
   Active: active (running) since Sun 2020-04-05 19:35:56 UTC; 1 weeks 0 days ago
 Main PID: 19694 (vultrdata)
    Tasks: 16 (limit: 4661)
   CGroup: /system.slice/vultrdata.service
           ├─19496 /opt/vultrdata/vultrdata --addr 10.1.2.3 --port 8888 --userdata
           └─19509 /opt/vultrdata/vultrdata --addr 10.1.2.3 --port 8888 --userdata
```

Or start, stop, restart it:

```
$ sudo systemctl start vultrdata.service
$ sudo systemctl stop vultrdata.service
$ sudo systemctl restart vultrdata.service
```

You can enable or disable starting the unit/service on system startup:

```
$ sudo systemctl enable vultrdata
$ sudo systemctl disable vultrdata
```

You can see/tail all systemd logs, or just for your service (unit):

```
$ sudo journalctl -f
$ sudo journalctl -f -u vultrdata
```


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